Influenza in Pregnancy: From the Maternal Lung to the Placenta and Fetus

Influenza in pregnancy is associated with a higher risk of severe respiratory disease and adverse maternal and perinatal outcomes, particularly later in gestation. This narrative review synthesizes evidence on epidemiology, pathophysiology, placental and fetal consequences, clinical presentation, diagnosis, antiviral management, and vaccination. Pregnancy involves dynamic immune adaptation together with reduced respiratory reserve, increased oxygen consumption, and cardiovascular changes that may amplify the effects of influenza pneumonia. Placental and fetal consequences appear to be mediated predominantly by maternal hypoxemia, fever, systemic inflammation, and hemodynamic disturbance; transplacental viral transmission is rare. Therefore, adverse fetal and neonatal outcomes are more closely linked to the severity and timing of maternal illness, placental dysfunction, and prematurity than to direct fetal infection. Prompt recognition is essential, and antiviral treatment should not await laboratory confirmation when influenza is suspected. Oseltamivir remains the preferred antiviral therapy and should be initiated as early as possible, including in patients presenting after 48 h with progressive or severe disease. Seasonal inactivated or recombinant influenza vaccination is the cornerstone of prevention, protecting both the mother and the infant through transplacental transfer of influenza-specific IgG. This integrated perspective supports vaccination, early diagnosis, and timely treatment to reduce maternal and perinatal risk.